In an optical device fabrication process, an optical device layer, e.g., composed of an n-type nitride semiconductor layer and a p-type nitride semiconductor layer, is formed on the front side of a single crystal substrate, such as a sapphire substrate, a silicon carbide (SiC) substrate or a gallium nitride (GaN) substrate, or on the front side of a glass substrate. The optical device layer is formed in a device area on the front side of the single crystal substrate or the glass substrate.
The optical device layer is partitioned by crossing division lines (also referred to as “streets”) to define separate regions where optical devices, such as light emitting diodes (LEDs) and laser diodes, are respectively formed. By providing the optical device layer on the front side of the single crystal substrate or the glass substrate, an optical device wafer is formed. The optical device wafer is separated, e.g., cut, along the division lines to divide the separate regions where the optical devices are formed, thereby obtaining the individual optical devices as chips or dies.
Substantially the same approach as detailed above is also adopted to obtain, for example, individual semiconductor devices, power devices, medical devices, electrical components or MEMS devices from substrates, such as single crystal substrates, glass substrates, compound substrates or polycrystalline substrates, with device areas in which these devices are formed.
The fabrication processes referred to above generally comprise a grinding step for adjusting the substrate thickness. The grinding step is performed from a back side of the substrate which is opposite to a substrate front side on which the device area is formed.
In particular, in order to achieve a size reduction of electronic equipment, the size of devices, such as optical devices, semiconductor devices, power devices, medical devices, electrical components or MEMS devices, has to be reduced. Hence, substrates having the devices formed thereon are ground in the above grinding step to thicknesses in the μm range, e.g., in the range from 30 to 200 μm.
However, in known device fabrication processes, problems may arise in the grinding step, such as damage to the substrate, e.g., by burning the substrate surface, or an unstable and slow grinding process, especially if the substrate is made of a material which is difficult to grind, such as glass, silicon (Si), gallium arsenide (GaAs), gallium nitride (GaN), gallium phosphide (GaP), indium arsenide (InAs), indium phosphide (InP), silicon carbide (SiC), silicon nitride (SiN), lithium tantalate (LT), lithium niobate (LN), sapphire (Al2O3), aluminium nitride (AlN), silicon oxide (SiO2) or the like.
Further, when substrates made of such difficult-to-process materials are ground, a considerable wear of the grinding means used occurs, resulting in a reduced service life of the grinding equipment, in particular, a grinding wheel included therein, and thus increased processing costs.
Hence, there remains a need for a method of processing a substrate which allows for the substrate to be processed in an efficient, reliable and cost-efficient manner.